Recently, as semiconductor devices have become highly integrated, it is desirable to have excellent characteristics in a small area in processes for isolating unit elements. This requires a decrease in the number of defects, the use of a good quality gate oxide film, and a development of techniques for isolating the element.
FIGS. 1A to 1D illustrate cross sectional views sequentially showing a conventional process of fabricating a semiconductor device. As shown in the drawings, after a hard mask material is coated on a wafer 10 to form a hard mask layer 11, a photoresist pattern 12 is formed on the hard mask layer 11. Following the application of the photoresist pattern 12, a mask for forming a trench isolation is formed by a dry etching process.
Next, the photoresist pattern 12 is removed, and a trench isolation 14 is formed by another dry etching process. Thereafter, an oxide film (not shown) is coated on the inside surface of the trench by an oxide film forming process.
The trench is then filled with a dielectric material, wherein the oxide film is coated thereon. By a Chemical Mechanical Polishing (CMP) process, an upper part of the dielectric material and the hard mask layer 11 are planarized until the hard mask layer 11 is removed. A cleaning process is then performed to eliminate entirely any hard mask material remaining on the wafer. Then, a well 17, a source region 15 and a drain region 16 are formed by a photoresist process and an ion implantation process, and finally a gate oxide film is formed. At this time, by many processes performed previously, especially the cleaning process, a divot 19 is generated.
After a polysilicon layer is coated on the entire wafer, a gate 21 is formed by a photoresist process and a dry etching process.
However, in such fabricating method described above, a poly residue or poly stringer 20 is produced due to the divot 19. The presence of the poly stringer 20 deteriorates the operational characteristics and reliability of the semiconductor device.